Cold workable and age-hardenable steel

ABSTRACT

A cold workable and age-hardenable steel includes weight percentages of carbon and manganese within an area enclosed by a line connecting a point P indicating zero weight % of carbon and 1.8 weight % of manganese, a point Q indicating 0.08 weight % of carbon and 0.5 weight % of manganese, and a point R indicating 0.08 weight % of carbon and zero % of manganese to a point S indicating zero weight % of carbon and zero weight % of manganese; less than 0.6 weight % of silicon; as agehardenability improving alloying metals more than 2.5 weight % of nickel and more than 0.6 weight % of aluminium or more than 2.5 weight % of nickel, more than 0.6 weight % of aluminum and more than 0.5 weight % of copper or more than 2.5 weight % of nickel, more than 0.6 weight % of aluminum and more than 0.5 weight % of titanium or more than 2.5 weight % of nickel, more than 0.6 weight % of aluminum, more than 0.5 weight % of copper and more than 0.5 weight % of titanium; the total amount of nickel and aluminum or nickel, aluminum and copper or nickel, aluminum and titanium or nickel, aluminium, copper and titanium being in the range of from 4.5 to 6.5 weight %; and the balance which is substantially iron and impurities. Added as ductility and temperability improving alloying metals may be at least one element selected from the group consisting of less than 2.5 weight % of chromium, less than 0.5 weight % of molybdenum, less than 0.5 weight % of tungsten, less than 0.5 weight % of cobalt, less than 0.5 weight % of beryllium and less than 0.01 weight % of both. Added as alloying metals for improving the fineness of the crystalline particles of the steel may be at least one element selected from the group consisting of less than 0.5 weight % the total amount of niobium and tantalum, less than 0.5 weight % of vanadium and less than 0.5 weight % of zirconium. Added as machinability improving alloying metals may be at least one element selected from the group consisting of less than 0.3 weight % of sulphur, less than 0.4 weight % of lead, less than 0.5 weight % of selenium, less than 0.3 weight % of tellurium and less than 0.3 weight % of bismuth.

United States Patent [191 Asada et al.

I Dec. 24, 1974 COLD WORKABLE AND AGE-HARDENABLE STEEL [75] Inventors: Chiaki Asada, Nagoya; Toshiyuki Watanabe, Nishio, both of Japan [73] Assignee: Daido Seiko Kabushiki Kaisha,

Minami-ku Nagoya Aichi Prefecture, Japan [22] Filed: Oct. 8, 1971 [21 Appl. No.: 187,825

[30] Foreign Application Priority Data Primary Examiner-Hyland Bizot Attorney, Agent, or Firm Wenderoth, Lind & Ponack [57] ABSTRACT A cold workable and age-hardenable steel includes weight percentages of carbon and manganese within an area enclosed by a line connecting a point P indicating zero weight of carbon and 1.8 weight of manganese, a point 0 indicating 0.08 weight of carbon and 0.5 weight of manganese, and a point R in- WEIGHT /a OF MANGANESE P16 0%, Mn 1 1 80%) dicating 0.08 weight of carbon and zero of manganese to a point S indicating zero weight of carbon and zero weight of manganese; less than 0.6 weight of silicon; as age-hardenability improving alloying metals more than 2.5 weight of nickel and more than 0.6 weight of aluminium or more than 2.5 weight of nickel, more than 0.6 weight-% of aluminum and more than 0.5 weight of copper or more than 2.5 weight of nickel, more than 0.6 weight of aluminum and more than 0.5 weight of titanium or more than 2.5 weight of nickel, more than 0.6 weight of aluminum, morethan 0.5 weight of copper and more than 0.5 weight of titanium; the totalamount of nickel and aluminum or nickel, aluminum and copper or nickel, aluminum and titanium or nickel,'aluminium, copper and titanium being in the range of from 4.5 to 6.5 weight and the balance which is substantially iron and impurities.

Added as ductility and temperability improving alloying metals may be at least one element selected from the group consisting of less than 2.5 weight of chromium, less than 0.5 weight of molybdenum, less than 0.5 weight of tungsten, less than 0.5 weight of cobalt, less than 0.5 weight of beryllium and less than 0.01 weight of both. Added as alloying metals for improving the fineness of the less than 0.3 weight of tellurium and less than 0.3

weight of bismuth.

1 Claim, 3 Drawing Figures PATENIEI] UEB24|974 WEIGHT 9/0 OF MANGANESE $856,514 sum NF 2 P(C I 0%, Mn11.80/o) R(C.'0.08%,Mni0%) S(C,MF1:O/L,) 0. 05 I 0110 WEIGHT /0 OF CARBON CHIAKI ASADA, and TOSHIYUKI WATANABE,

INVENTOR S BY Madam ATTORNEY S PATENTED [E824 I974 sum NF 2 FIG. 2

mmmzomql mmmxo Du E T N E (\C A F 3 0 m F 0 -m 8 -0 O 6 -O 0 4 0 O 2 -0 O 0 0 0 w m 0 0 0 w w w e m 4 w m DEPTH MEASURED FROM THE SURFACE" OF THE STEELS (mm) CHIAKI ASADA and TOSHIYUKI WATANABE, INVENTOIE fibAzylnrmlwwpmu ATTORNEY COLD WORKABLE AND AGE-HARDENABLE STEEL DETAILED EXPLANATION OF INVENTION This invention relates to cold workable and agehardenable Ni-Al type, Ni-Al-Cu type, Ni-Al-Ti type and Ni-Al-Cu-Ti type steels which are machinable with easiness and have high ductility under the solution treatments.

Business machines such as data-processing machines and complicated articles such as racks, gears, arms, stoppers and carriages used in making a computer are made by using a case hardening steel and then they are heat-treated for hardening the case hardening steel. Also such business machines and such complicated articles are made of a heat-treated band steel. In such a case, the case hardening steel has a defect so that it has strain after it was heat-treated, and also the heat treated band steel has a defect so that it is difficult to work it into such a complicated article.

It is preferable to use an age-hardenable steel, which has less strain after it was heat-treated, for making such a business machine and such a complicated article but the prior known age-hardenable steels do not always give the satisfactory results in making the business machines and the complicated articles.

The inventors have investigated for removing the above mentioned defects form the prior known steels and have discovered cold workable and age-hardenable steels which are improved in their cold-workability by reducing their hardness under the solution treatments and can be hardened by age-treatment and have little strain after they were heat-treated.

It is an object of this invention to provide a cold workable and agehardenable steel consisting essentially of weight percentages of carbon and manganese within an area enclosed by a line connecting points P, Q and R to a point S as shown in the accompanying FIG. 1; less than 0.6 weight of silicon; as age-hardenability improving alloying metals more than 2.5 weight 7r of nickel and more than 0.6 weight of aluminum or more than 2.5 weight 76 of nickel, more than 0.6 weight of aluminum and more than 0.5 weight 7c of copper or more than 2.5 weight of nickel, more than 0.6 weight 71 of aluminum and more than 0.5 weight of titanium or more than 2.5 weight of nickel, more than 0.6 weight of aluminum, more than 0.5 weight of copper and more than 0.5 weight of titanium; the total amount of nickel and aluminum or nickel, aluminum and copper or nickel, aluminum and titanium or nickel, aluminum, copper and titanium being in the range of from 4.5 to 6.5 weght and the balance which is substantially iron and impurities, said point P indicating zero weight of carbon and 1.8 weight of manganese, said point Q indicating 0.08 wieght of carbon and 0.5 weight of manganese, said point R indicating 0.08 weight of carbon and zero weight 7: of manganese and said point S indicating zero weight of carbon and zero weight of manganese.

Also, it is another object of this invention to provide a cold workable and age-hardenable steel consisting essentially of weight percentages of carbon and manganese within an area enclosed by a line connecting points P. Q and R to a point S as shown in the accompanying FIG. 1; less than 0.6 weight 7: of silicon; as age-hardenability improving alloying metals more than 2.5 weight of nickel and more than 0.6 weight of aluminum or more than 2.5 weight of nickel, more than 0.6 weight of aluminum and more than 0.5 weight of copper or more than 2.5 weight 7r of nickel, more than 0.6 weight of aluminum and more than 0.5 weight of titanium or more than 2.5 weight of nickel, more than 0.6 .weight /r of aluminum, more than 0.5 weight of copper and more than 0.5 weight of titanium; the total amount of nickel and aluminum or nickel, aluminum and copper or nickel,

aluminum and titanium or nickel, aluminum, copper and titanium being in the range of from 4.5 to 6.5 weight and the balance which is substantially iron and impurities in combination with at least one ofductility and temperability improving alloying metals alone or at least one of alloying metals alone for improving the fineness of the crystalline particles of said steel and at least one of machinability improving alloying metals alone or in combination with at least two metals selected from said ductility and temperability improving alloying metal, said alloying metal for improving the fineness of the crystalline particles of said steel and said machinability improving alloying metal, said point P indicating zero weight of carbon and 1.8 weight of manganese, said point Q indicating 0.08 weight of carbon and 0.5 weight of manganese, said point R indicating 0.08 weight of carbon and zero weight of manganese and said point S indicating zero weight of carbon and zero weight 7: of manganese.

The reasons why carbon, maganese, silicon, age-hardenability improving alloying metals, ductility and temperability improving alloying metals, alloying metals for improving the fineness of the crystalline particles of the steel and machinability improving alloying metals are defined as the components and also in their amounts in accordance with this invention are explained hereinafter.-

1. Carbon and Manganese:

The cold workability which is determined on the basis of the ltight-bending of the steel is varied depending upon not only the solution treated hardness but the contents of carbon and maganese, and therefore it'is preferable to use carbon and manganese in the amounts as defined within the area enclosed by the line connecting the points P, Q and R to the point S as shown in the accompanying FIG. 1 showing carbon versus manganese. This is fully explained as the descrip tion goes on.

2. Silicon:

A small amount of silicon is essential for conducting the smelting technique but a larger amount of silicon impairs the ductility and the cold workability of steels and therefore the content of silicon is defined to less than 0.6 weight percentage.

3. Nickel:

Nickel is an alloying element for producing a Ni-Al when it is added into steels in an amount of below 2.5

weight percentages. 4. Aluminum:

Aluminum is an alloying element for producing an Al-Ni alloy and an Al-Ti alloy, and also it is an essential alloying element forimproving the age-hardenability of steels by the synergistic actions and effects between Al proving the age-hardenability of the steels and it is used as an essential element for strengthening the steels by the synergistic actions and effects between Cu and depositions resulted by the presence of nickel, aluminum and titanium. It is preferable to use copper in an amount of above 0.5 weight percentage.

6. Titanium:

Titanium is an alloying element for producing a metal compound between Ti and Ni or Ti and Al and it is used as an essential element for improving the age-hardenability of steels by the synergistic actions and effects between Ti and Cu. It is preferable to use titanium in an amount of above 0.5 weight percentage.

It is obvious from the data as shown in Table 2 that the total amount of the age-hardenability improving alloying metals which are added in the cold workable and age-hardenable steel of this invention in combination of Niand Al or Ni, Al and Cu or Ni, Al and Ti or Ni, Al, Cu and Ti is required to limit to the lower content of 4.5 weight percentages for obtaining the intended Vickers age-hardness of above 300. However, if the age-hardenability improving alloying metals are used in a larger amount of above 6.5 weight percentages, they become expensive and also in some cases aluminum, copper and titanium impede the output of the steels and therefore the total amount of the age-hardenability improving alloying metals are defined within the range of from 4.5 to 6.5 weight percentages.

7. Chromium, molybdenum, tungsten, cobalt, beryllium and boron:

These metals can be used alone or in combination for improving the ductility and the resistance against the softening of the cold workable and age-hardenable steel of this invention when less than 2.5 weight of chromium, less than 0.5 weight of molybdenum, less of cobalt and less than 0.5 weight 7r of beryllium are incorporated with said steel but they impeded the cold workability of the steel and become expensive when they are used in a larger amount. Also, the cold workable and age-hardenable steel of this invention is improved markedly in its temperability when a small amount of boron is incorporated with said steel but the ductility and the output of the steel are impeded when boron is incorporated with the steel in an excess amount. Therefore, it is preferable to use boron in an amount of below 0.01 weight percentage.

8. Niobium, tantalum, vanadium and zirconium:

These metals can be used for improving the cold workability under the conditions of solution treatment and the fineness of the crystalline particles of the cold workable and age-hardenable steel of this invention but they become expensive and the output of the steel is impeded when they are used in a larger amount. Therefore, the total amount of niobium and tantalum is defined to less than 0.5 weight percentage and vanadium and zirconium are defined to less than 0.5 weight percentage respectively.

9. Sulphur, lead, selenium, tellurium and bismuth:

These metals can be used for improving the machinability and retaining the age-hardenability of the cold workable and age-hardenable steel of this invention but the steel is impeded in its ductility and workability and it tneds to become brittle when such metals are incorporated with the steel in a larger amount. Therefore it is preferable to use sulphur, lead, selenium, tellurium and bismuth in an amount of below 0.3 weight 7r, below 0.4 weight below 0.5 weight 71 below 0.3 weight 7! and below 0.3 weight 7( respectively.

This invention is illustrated by the following Examples.

Referring to Table 1, it shows various kinds of steels designated by the signs M(or Nal NA2, D, E, NAK-Z, NAK3, N(or NAT-l NAT-2, A (or NAK- T-l B, C, NAKT-2, N28. NAKT-3, F, G(or than 0.5 weight of tungsten, less than 0.5 weight 4O NAK-l )1 Hi J, K and Table l Compositions of Steels 7r Signs of Stee C Si Mn P S Ni Al Cu Ti Others M or NAI 0.01 0.09 1.20 0.007 0.012 3.65 1.10 0.15

2 0.009 0.10 1.25 0.010 0.010 3.56 1.04 0.13 Cr 1 0.50 N3 0.01 0.008 1.19 0.009 0.008 3.52 1.08 0.16 Nb Ttl 1 0.08 NA-2 0.01 0.06 1.18 0.010 0.005 3.67 1.09 0.10 se 0.05 N5 0.011 0.09 1.21 0.011 0.007 3.40 0.98 0.09 Cr 10.50.V 20.15 N6 0.008 0.11 1.24 0.013 0.009 3.35 1.01 0.13 Cr 1 0.45.Phl(1.15 N7 0.01 0.12 1.17 0.020 0.011 3.60 1.05 0.08 Nb I 0.02.1b20.15 N8 0.007 0.15 1.23 0.018- 0.103 3.55 1.03 0.07 M0 0.2, V 20.1 N9 (1.01 0.10 1.24 0.011 0.021 3.25 0.98 1.05 D 0.03 0.06 0.52 0.003 0.019 3.14 0.98 0.90 Be 2 0.01 E 0.07 0.15 0.52 0.003 0.008 3.34 0.96 1.04 M0 2 (1.20 N11 002 0.13 0.78 0.009 0.012 3.45 1.05 1.01 Nb 2 0.06 NAK-2 0.04 0.10 1.07 0.004 0.090 3.35 1.08 0.98 N13 0.06 0.13 0.65 I 0.010 0.010 3.10 1.02 0.95 M0 2 0.20.V10.10 N14 0.01 0.07 1.25 0.005 0.094 3.25 0.97 0.98 M0 2 0.15 N15 0.05 0.08 0.49 0.009 0,084 3.40 0.94 0.91 V I 0.15 NAK-3 0.03 0.25 0.99 0.008 0.108 3.23 1.12 1.10 M0 1 0.15,V:0.10 N or NAT-1 0.05 0.03 0.70 0.010 0.007 3.85 0.90 0.01 1 05 N18 0.03 0.02 0.65 0.010 (1.010 3.64 0.98 0.05 l 15 M0 1 0.21 N19 0.01 0.14 0.84 0.008 0.011 3.45 0.97 0.10 1 01 N1) 2 0.02 N20 0.01 0.12 0.45 0.013 0.016 3.50 1.05 0.05 0.98 Pb I 0.14 N21 0.009 0.09 0.75 0.017 0.018 3.71 1.10 0.13 1.13 Cr 1 0.45,V20.10 N22 0.02 0.14 1.12 0.013 0.012 3.49 1.08 0.10 1.15 MO I 0.12,Pl)!0.10 NAT-2 0.03 0.04 1.30 0.015 0.009 3.51 1.02 0.05 1.10 Nb Ta 1 0.20

N24 0.02 0.07 1.10 0.013 0.075 3.21 0.95 0.11 0.95 B Z 0.001,V10.10 A or NAKT- l 0.01 0.08 1.00 0.003 0.008 3.14 0.99 0.90 1.10 13 0.02 0.21 1.49 0.013 0.009 3.05 0.93 0.93 1.06 C I 0.05 0.11 0.94 0.004 0.009 3.05 1.00 0.87 1.03

Table l-Continued Compositions of Steels 7r 1 Signs of 516815 C Si Mn P S Ni Al Cu Ti Others N26 0.03 0.14 1 0.97 0.015 0.010 3.35 1.07 0.95 1.15 B 0.003 N27 0.01 0.16 0.99 0.016 0.015 3.25 0.96 1.05 0.98 V 0.13 NAKT-Z 0.02 0.09 1.05 0.003 0.008 3.20 0.95 1.01 l.02 Pb 0.15 N28 0.01 0.11 1.10 0.005 0.102 3.10 0.98 0.97 102 N29 0.01 0.13 1.25 0.016 0.010 3.25 0.95 1.10 1.12 Mo 0.25.V:0.1 NAKT-3 0.01 0.11 1.10 0.005 0.102 3.10 0.98 0.97 1.02 Cr 0.87 N31 0.008 0.16 1.45 0.010 0.095 3.35 1.11 0.98 1.13 V 0.10 N32 0.01 0.13 1.15 0.017 0.084 3.10 1.05 0.97 1.03 V 0.10.Cr:0.56

F 0.05 0.07 1.22 0.003 0.009 3.08 1.02 0.87 1.10 G or NAK-l 0.03 0.41 1.53 0.004 0.010 3.27 1.20 1.05 H 0.08 0.06 1.70 0.003 0.024 3.14 1.02 0.003 1.06 1 0.07 0.14 0.74 0.003 0.009 3.22 1.01 1.00 J 0.09 0.14 0.50 0.003 0.010 3.22 0.91 1.01 K 0.05 0.06 1.64 0.005 0.008 3.13 1.16 0.05 L 0.09 0.08 1.50 0.003 0.007 0.06 0.002 0.98

It should be noted from Table 1 that the steels M, N, NATK-l B, c, NAKT-Z, N28and NAKT-3 are the A and G are the same as the steels NA-1, NAT1, NAKT-1 and NAK-l respectively. Also it should be noted from Table 1 that the steels M (or NA-l N A-2, D, E. NAK2, NAK3. N(or NAT-l NAT-2, A (or NAKT-l), B, C, NAKT-Z. N28 and NAKT-3 are the cold workable and age-hardenable steels of this invention and the steels F, G. (or NAK-l), H, l, J, K and L are the comparative steels. Still further, it should be noted that the steels M and NA2 are the cold workable and age-hardenable NiAl type steels; the steels D, E, NAK2 and NAK-3 are the cold workable and agehardenable Ni-Al-Cu type steels; and steels N(or NAT-1) and NAT-2 are the cold workable and age- -hardenable Ni-A1-Ti type steels; and the steels A(or cold workable and age-hardenable Ni'Al-Cu-Ti type steels of this invention.

Test samples of the steels as shown in Table l were subjected to the solution treatment at 900C for 10 minutes, followed by cooling them in oil and then the treated test samples were tested for ltight-bending and machinability. Further, the treated test samples were age-treated at 525C for 5 hours. The cold workability of the steels which were subjected to the solution treatment was determined by observing the presence or the absence of cracks on the bent part of each of the test samples after they were tested for l80tight bending in the direction along the rolling of the steels. The test results are give in Table 2.

Table 2 Signs of Total sum Solution Life of Age- Tensile Steels of Ni. Al, treated tightcutting hardness strength Cu. Ti ("/(1 hardness bending tool(in (Vickers) after age (Vickers) minutes) treated(kg/mm M or NA-l 4.90 188 good 207 355 118.0 N2 4.73 189 good 356 119.5 N3 4.76 190 good 203 359 120.0 NA-2 4.86 179 good 283 360 125.0 N5 4.47 193 good 371 1210 N6 4.49 188 good .357 1190 N7 4.73 191 good 265 356 115.3 N8 4.65 192 good 253 361 120.1 N9 5.28 good 363 121.0 D 5.02 good 366 122.0 E 5.34 230 good 350 118.3 -N11 5.51 197 good 351 117.0 NAK-Z 5.41 195 good 275 380 127.3 N13 507 209 good 395 131.7 N14 5.20 206 good 394 131.3 N15 5.25 201 good 385 128.0 NAK-3 5.50 225 good 258 445 148.7 N or NAT-1 5.81 205 good 141 420 140.0 N18 5.82 210 good 415 138.5 N19 5.53 220 good 425 140.1 N20 5.58 207 good 410 136.8 N21 6.07 225 good 441 147.0 N22 5.82 218 good 430 143.0 NAT-2 5.68 215 good 237 451 154.1 N24 522 235 good 455 151.8 A or NAKT-l 6.13 180 good 180 450 155.3 8 5.97 185 good 490 160.2 C 5.95 175 good 460 153.0 N26 6.52 190 good 467 155.5 N27 6.24 179 good 441 147.0 NAKT-Z 6.18 178 good 270 451 155.7 N28 6.07 175 good 260 455 150.1 N29 6.42 182 good 445 148.5 NAKT3 6.07 175 good 260 455 151.0 N31 6.57 184 good 460 153.0 N32 615 195 good 475 155.0 F 6.07 180 had 480 Table 2-Continued Signs of Total sum Solution 180 Life of Age- Tensile Steels of Ni, Al. treated tightcutting hardness strength Cu, Ti /l) hardness bending tool(in (Vickers) after age (Vickers) minutes) treatedlkg/mm) G or NAK-l 5.52 200 bad 360 H 5.22 175 had 325 l 5.23 230 had 360 .l 5.14 335 had 365 K 4.34 175 good 230 l 1.04 150 good 180 It is noted that the life of the cutting tool was determined when the tool lost its cutting ability. Also it is noted that the cutting test was carried out by using a SKl-l-9 slitting saw as the cutting tool and the test samples were fed by using a feeding gear having a 0.0174

mm/tooth and they were cut into a 0.8 mm depth at the cutting speed of 70 meters per minute.

It is obvious for the data as shown in Table 2 that the 180 tight-bending of the steels is improved as the solution treated hardness of the steels decreases but the steels are required to have a very low solution treated hardness for securing the reliable 180 tight-bending.

In accordance with this invention, the total sum of the age-hardenability improving alloying metals (Ni, Al

Cu and Ti) must be kept at the 4.7 weight percentages or more for securing the age-hardness equivalent to or of above 300 vickers hardness of the cold workable and age-hardenable steel and-therefore the solution treated hardness of sucha cold workable and age-hardenable steel can not unlimitedly be reduced by decreasing the 35.

total amount of the age-hardenability improving alloying metals. Also the solution treated hardness of the cold workable and age-hardenable steel of this invention is required to be kept at 175 Vickers hardness or more for securing the age'hardness of about 300 Vick- 40 ers hardness. Within the range of such a Vickers hardness, the solution treated hardness is not co-related to the 180 tight-bending as shown in Table 2.

Referring to FIG. 1, it shows the relationshiip between the I80 tight-bending of the test samples and In the FIG. 1, the white marked points indicate'that the 180tight-bending of the test samples is good and also the black marked points indicate that the 180tight-bending of the test samples is bad. It is obvious from the FIG. 1 that the 180 tight-bending of the cold workable and age-hardenable steels of this inven- 6 tion is strongly co-related to the amounts of carbon and manganese contained in such steels and also that it is possible to secure the l80tight-bending of such steels when they are fallen within the area enclosed by the line connecting the points P, Q and R to the point 5, and they contain less than 0.08 weight 7r of carbon and less than 1.8 weight of manganese.

It was also recognized that the use of a suitable amount of the machinability improving alloying metals can improve remarkedly the life of the cutting tools without affecting the ltight-bending and the agehardness of the cold workable and age-hardenable steels of this invention. Still further, it was recognized that the use of a suitable amount of the ductility and temperability improving alloying metals and the alloying metals for improving the fineness of the crystalline particles can improve the strength of the cold workable and age-hardenable steels of this invention without affecting the 180tight-bending, the age-hardness and the machinability of such steels. g

In the FIG. 2, the test results are shown after the steel A(or NAKT-l) was treated with a liquid nitriding agent, which is sold under the trade name of NH-360 by Nisshin Kagaku Kaisha, at 520C for 2 hours.

In the FIG. 3, the-curve 1 shows the test results after the steel A(or NAKT-l) was treated at 570C for minutes by using a tufftriding method. The Curves 2 and 3 show the test results after the steel A(or NAK- T-l was treated at 570C for 60 minutes and 30 minutes respectively by using the tufftriding method. Also the curve 4 shows the test results after the steel G(or NAK-l was treated at 570Cfor 180 minutes by using the tufftriding method.

As you can see from the foregoing, it is the critical essential features of the cold workable and gehardenable steel of this invention to contain less than I 0.08 weight of carbon and less than 1.8 weight of maganese and to fall within the area as indicated in the 0 FIG. 1. Also, it is the critical essential features of the cold workable and age-hardenable steel of this invention to contain the age-hardenability improving alloying metals in combination of Ni and Al or Ni, Al and Cu or Ni, Al and Ti or Ni, Al, Cu and Ti in which Ni is more than 2.5 weight Al is more than 0.6 weight Cu is more than 0.5 weight 7: and Ti is more than 0.5 weight and the total amount of the age-hardenability improving alloying metals is in the range of from 4.5 to 6.5 weight percentages.

Also the steel A(or NAKT-l was tested for the 180 tight-bending by using various kinds of the solution treatments and the inventors have found that the solution treatments have no effect on the 180 tight bending of the steel A. The test results are given in Table 3.

Table 3 Temp. ("C) used Time(minutes) Solution 180 tightage-hardness for the used for the treated bending after treated solution solution treathardness at 525C for treatments ment. (Vickers) 5 hours Water cooling (Vickers) is used 950 l 184 good 450 5 195 good 460 900 l 180 good 450 5 182 good l 800 1 I77 good 445 5 I80 good 452 700 l 175 good 440 5 180 good 447 650 l 177 good 440 5 180 good 435 Further the steel A (or NAKT-1) was cut into test samples having the size of 1 mm thickness X 30 mm width X 105 mm length and the test samples were bent by the angle of 90 and then the variation of angle was observed after they were age-treated. It was found that the test samples had a little strain resulted by the thermal treatments. The test results are given in Table 4. The test results are compared with much strain of the commercial tempered and annealed steels without showing the data after they were thermally treated.

Table 4 nium, tellurium and bismuth as the machinability improving alloying metals with the materials. Thus, it is easily understood that the cold workable and agehardenable steels of this invention can widely be used as the structural steels having high machinability and less thermal strain and they are practically useful steels.

What we claim is that:

l. A cold workable and age-hardienable steel, charac terized in that it consists essentially of the weight percentages of carbon and manganese within the area en- Bending radiusestmillimeters) The sign l. indicates that the test samples were bent in the direction along the rolling of the steel A. The sign T indicates that the test samples were bent in the direction perpendicular to the rolling of the steel A.

it is obvious from the foregoing that the cold workable and age-hardenble steels of this invention have been developed for obtaining the materials, which are easily workable by pressing, extruding, deep drawing, heading or cutting by applying the cold workability to the steels under the conditions of the solution treatment, having the age-hardness of above 300 Vickers hardness and the improved machinability after the materials were age-treated. In order to achieve the intended purpose, the specified amount of Ni and Al or Ni, Al and Cu or Ni, Aland Ti or Ni, Al, Cu and Ti is added to the steels as the age-hardenability improving alloying metals and also the contents of carbon and manganese are defined as mentioned above for securing the cold workability of the materials. Still further, the ductility and temperability of the materials, the fineness of the crystalline particles of the materials and the machinability of the materials are improved by incorporating the specified amount ofchromium, molybdenum, tungsten. cobalt, beryllium and boron as the ductility and temperability improving alloying metals; the specified amount of niobium, tantalum, vanadium and zirconium the fineness improvingv alloying metals; and the specified-amount of sulphur, lead, seleclosed by the line connecting points P, Q and R to the point S as shown in the accompanying FIG. 1; an effective amount up to 0.6 weight of silicon, and, as agehardenability improving alloying metals, more than 2.5 weight of nickel, more than 0.6 weight 7: of aluminum, more than 0.5 weight of copper and more than 0.5 weight of titanium, the total amount of nickel, aluminum, copper and titanium being inthe range of from 4.6 to 6.5 weight said point P indicating zero weight 7: of carbon and 1.8 weight 7r of manganese, said point Q indicating 0.0 8 weight 72 of carbon and 0.5 weight of manganese, said point R indicating 0.08 weight of carbon and zero weight of manganese and said point S indicating zero weight 7: of car bon and zero weight 7: of manganese, and further consisting of, as alloying metals for improving the fineness of the crystalline particles of said steel, at least one element selected from the group consisting of an effective amount up to 0.3 weight 7: of the total amount of mo bium and tantalum, an effective amount up to 0.5 weight 71 of vanadium and an effective amount up to 0.5 weight 7 of zirconium. 

1. A COLD WORKABLE AND AGE-HARDENABLE STEEL, CHARACTERIZED IN THAT IT CONSISTS ESSENTIALLY OF THE WEIGHT PERCENTAGES OF CARBON AND MANGANESE WITHIN THE AREA ENCLOSED BY THE LINE CONNECTING POINTS P, Q AND R TO THE POINT S AS SHOWN IN THE ACCOMPANYING FIG.1; AN EFFECTIVE AMOUNT UP TO 0.6 WEIGHT % OF SILICON, AND AS AGE-HARDENABILITY IMPROVING ALLOYING METALS, MORE THAN 2.5 WEIGHT % OF NICKEL, MORE THAN 0.6 WEIGHT % OF ALUMINUM, MORE THAN 0.5 WEIGHT % OF COPPER AND MORE THAN 0.5 WEIGHT % OF TITANIUM, THE TOTAL AMOUNT OF NICKEL, ALUMINUM, COPPER AND TITANIUM BEING IN THE RANGE OF FROM 4.6 TO 6.5 WEIGHT %, SAID POINT P INDICATING ZERO WEIGHT % OF CARBON AND 1.8 WEIGHT % OF MANGANESE, SAID POINT Q INDICATING 0.08 WEIGHT % OF CARBON AND 0.5 WEIGHT % OF MANGANESE, SAID POINT R INDICATING 0.08 WEIGHT % OF CARBON AND ZERO WEIGHT % OF MANGANESE AND SAID POINT S INDICATING ZERO WEIGHT % OF BON AND ZERO WEIGHT % OF MANGANESE, AND FURTHER CONSISTING OF, AS ALLOYING METALS FOR IMPROVING THE FINENESS OF THE CRYSTALLINE PARTICLES OF SAID STEEL, AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF AN EFFECTIVE AMOUNT UP TO 0.3 WEIGHT % OF THE TOTAL AMOUNT OF NIOBIUM AND TANTALUM, AN EFFECTIVE AMOUNT UP TO 0.5 WEIGHT % OF VANADIUM AND AN EFFECTIVE AMOUNT UP TO 0.5 WEIGHT % OF ZIRCONIUM. 